It has been found that tanks of the aforementioned type, i.e. with a cross section as a figure of eight and with two simply rotating stirring devices, are highly suitable for a desirable treatment of the mass of cheese coagulum which is produced in the tank, suspended in whey, where it is important that the coagulum grains be kept uniformly suspended in the whey, as they will otherwise sink down and choke the outlet. By the end of their stay in the tank the grains are to be pumped out together with the whey for delivery to a further processing equipment, and it is desirable that this delivery can take place as an even flow, without occurance of any concentration of the grains towards the end of the outflow from the container, as it may otherwise be difficult to achieve an effective emptying of the container. Also for this reason it is important that the stirring devices operate quite closely to the bottom surface.
However, the final delivery from the bottom area raises problems. An effective final outflow is conditioned by the bottom areas beneath the stirring devices not being horizontally disposed, as they should slope downwardly towards the outlet, this most naturally being obtained by shaping the bottom areas conically, such that they form a downwardly narrowing well adjacent to each of the stirring shafts. The stirring blades may still operate immediately above the bottom surfaces, as they can be shaped with their lower edges extending outwardly and upwardly inclined corresponding to the bottom shape of the single container sections. Only it has to be accepted hereby that in the transition area between the two container sections a bottom elevation will occur. This elevation is a natural consequence of the intersection between the two conical bottom areas, and it makes no change in the fact that a very efficient final emptying of the two conical bottom areas is achievable. However, as known by the experts, the elevation results in the disadvantage that is required to make use of two mutually separated outlets from the tank, which can cause troubles, particularly towards the end of the emptying, where one bottom section may run dry before the other or even be found to be totally blocked by a compact mass of coagulum in the entire respective bottom area, thereby resulting in a considerable waste of coagulum.
It should be briefly mentioned that in curdling tanks not only a stirring is to be effected, but also, at an intermediate phase, a cutting function which is achieved, among things, by reversing the direction of rotation of the stirring devices, whereby a stirring grating is changed into a cutting grating operating to cut the coagulated milk mass into coagulum pieces that deliver whey from the cut surfaces and thereby shrink considerably, so as to form the said coagulum grains in the surrounding whey. Coagulum parts that are left uncut will instead be converted into a crumbled mass, which can subsequently be difficult to separate from the whey, and it is important, therefore, that the stirring and cutting blades or gratings reach as far as possible towards the side and bottom faces of the tank.
In this respect an entirely flat bottom is ideal, but such a bottom gives rise to special emptying problems, because a considerable tilting of the tank will be required for ensuring an efficient emptying through an outlet, and this is why other possibilities such as the first mentioned arrangement have been tried, though then with a required acceptance of other disadvantage.